Dependence of the terahertz wave frequency upconversion detection characteristics on the pumping pulse energy

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Terahertz (THz) frequency upconversion detection is a promising method in the field of THz measurement. This paper focuses on the dependence of the THz frequency upconversion detection characteristics based on the stimulated polariton scattering (SPS) effect in lithium niobite (LN) crystal on the pumping pulse energy. It was found that optimal pumping pulse energy exists, which leads to the largest ratio of the upconverted Stokes signal to the background clutter. In the theoretical part, the background clutter is divided into two parts: the amplified spontaneous Stokes fluorescence and other background clutter. The expressions for the upconverted Stokes signal and amplified spontaneous Stokes fluorescence are derived, and the terahertz wave frequency upconversion detection characteristics varying with the pumping pulse energy are successfully explained.